Tinsel ribbon conductor with tubed polymer insulation and method for making same

ABSTRACT

THIS DISCLOSURE DESCRIBES A TELEPHONE CORD STRUCTURE CONSISTING OF A PLURALITY OF TUBED POLYMER INSULATED TINSEL CONDUCTORS ENCLOSED IN A POLYMER OUTER JACEKT. A METHOD FOR PRODUCING THE CORD INCLUDES THE STEPS OF REHEATING AND STRETCHING THE POLYMER INSULATION TO ACHIEVE INCREASED TENSILE MODULUS AND STRAIN MEMORY AND TO GAIN ADDITIONAL CONDUCTOR LENGTH.   D R A W I N G

E. R. cocco 3,553,042 TINSEL RIBBON CONDUCTOR WITH TUBED POLYMER I Jan. 5, 1971 INSULATION AND METHOD FOR MAKING SAME Filed Dec. 27, 1968 INVENTOR ER. COCCO BY ATTORNEY United States Patent 3,553,042 TINSEL RIBBON CONDUCTOR WITH TUBED POLYMER INSULATION AND METHOD FOR MAKING SAME Eugene R. Cocco, Baltimore, Md., assignor to Bell Telephone Laboratories, Incorporated, Murray Hill and Berkeley Heights, N.J., a corporation of New York Filed Dec. 27, 1968, Ser. No. 787,377 Int. Cl. H01b 13/14 US. Cl. 156-50 6 Claims ABSTRACT OF THE DISCLOSURE This disclosure describes a telephone cord structure consisting of a plurality of tubed polymer insulated tinsel conductors enclosed in a polymer outer jacket. A method for producing the cord includes the steps of reheating and stretching the polymer insulation to achieve increased tensile modulus and strain memory and to gain additional conductor length.

FIELD OF THE INVENTION This invention concerns electric communication cordage and manufacturing methods; and more particularly involves a method for producing insulated tinsel conductor cordage of an unusually small diameter which, as a coiled cord, exhibits substantially improved tensile modulus and strain memory.

BACKGROUND OF THE INVENTION The term cord in telephone parlance refers to the insulated conductor member that connects a telephone instrument to a wall or floor jack box or to a switchboard; and includes handset cordage also. Present versions of these cords can be criticized on several bases. 'For one, their diameter is greater than considerations of insulation alone would require. This traces to the fact that the polyvinyl chloride outer jacket which houses the insulated conductors supplies the retractility for coiled cordage as well as mechanical protection. Both these functions dictate a thick and relatively expensive bulk of polyvinyl chloride. As telephone sets become smaller in size, these relatively large diameter cords become increasingly unattractive from an aesthetic standpoint.

In applicants earlier patent application Ser. No. 679,016 filed Oct. 30, 19.67, and now abandoned, a cord structure of greatly reduced cross section but with enhanced retractility was suggested in which the retractility was supplied by the primary conductor insulation, preferably a polyamide, thus permitting use of an outer jacket greatly reduced in thickness and diameter.

One aspect of the present invention is directed to the construction of such cords; and particularly to steps that simplify their manufacture by eliminating any need for a yarn knitted barrier. The steps further provide still greater tensile modulus and strain memory for enhanced retractility; and as a bonus also result in added conductor length without added conductor structure.

One object of the invention accordingly is to achieve smaller diameter telephone cordage for both aesthetic and economic reasons.

A second object of the invention is to produce telephone cordage with enhanced tensile modulus and strain memory.

A third object of the invention is to improve the re tractility characteristics of coiled telephone cords.

- A further object of the invention is to reduce the cost of such cordage.

3,553,042 Patented Jan. 5, 1971 The invention achieves these and other objects in a manufacturing process including the steps of tubing polymer insulation directly over tinsel conductors and thereafter reheating and concurrently stretching the member under controlled conditions.

In one illustrative embodiment the invention is practiced by adding a heat chamber, a cooling trough, and an added take-up to a standard extrusion line. Pursuant to one aspect of the invention, stretching of the tubed polymer insulation over the tinsel conductor is made possible by carefully controlling the original tube dimensions so that the tinsel ribbon edge will at no time bind on the surrounding insulation. The applied stretch is in the range of a 4 to 5 percent increase of length. The stretched cordage when coiled exhibits an enhanced retractility and yet is as durable as the unstretched version.

The invention, its further objects, features and advantages will be readily apprehended from a reading of the description to follow of an illustrative embodiment.

DESCRIPTION OF THE DRAWING FIG. 1 is a schematic perspective diagram of a manufacturing process including the inventive steps;

FIG. 2 is a schematic side perspective diagram showing insulated tinsel conductors used in cordage; and

FIG. 3 shows such cordage being given a helical set.

DETAILED DESCRIPTION OF AN ILLUSTRATIVE EMBODIMENT FIG. 1 depicts a production line in which the apparatus needed to practice the inventive method has been included. A reel 1 serves as a source of tinsel conductor 2. This structure shown also in FIGS. 2 and 3 in greater detail is routinely used in cord manufacture and can take numerous configurations, among these being single and double lay helices, butting edges, overlapping edges, and more than one helix per lay. The tinsel ribbon on which such conductors are made typically is .020 inch wide and .001 inch thick. The tinsel ribbon structure itself comprises one or more ribbons wound upon a support unit such as a cotton strand or a polymer monofilament.

Tinsel conductor 2 is fed around idler pulleys 3 and 4 and into a tubing mill 5. The latter consists of a hopper 6, and an extruder crosshead 7 that applies in conventional fashion a tube of specified diameter and thickness onto tinsel conductor 2 as it passes through the head 7. The other details of tube mill 5 are not important, its function simply being to tube extrude, rather than pressure extrude, an insulative covering onto tinsel conductor 2.

Insulation, such as shown as item 8 in FIGS. 2 and 3, is approximately .003 inch greater in inside diameter than the outside diameter of tinsel conductor 2. The clearance pursuant to one aspect of the invention later permits the insulation 8 to be drawn down closer to tinsel conductor 2 at a later stage. The thickness of insulation 8 typically is .007 inch; and its material advantageously is a polyamide, a polypropylene, a polyethylene, or an equivalent thereof characterized by a very high tensile modulus and strain memory. In this context, the term tensile modulus means the ratio of stress to strain in the elastic range of the insulating polymer; and the term strain memory means the capacity of the insulating polymer to recover its original helical set after extensions up to several times the original retracted length.

The insulated tinsel conductor next is fed through a cooling trough 9 in which water circulates through a system not shown. Exiting cooling trough 9, the insulated tinsel conductor feeds around the main take-up capstan 10 and over an idler pulley 11. A second take-up capstan 12 situated downline from capstan is, pursuant to the invention, driven at a speed slightly in excess of capstan 10. Thus, the insulated ribbon in traveling between capstans 10 and 12, experiences a stretch.

The stretch serves two purposes: first, concurrently with the stretching, the insulated conductor is passed through a heat chamber 13 that reheats the insulated conductor from the temperature of 80 F. to 160 F., depending on polymer used, at which it exited from trough 9 to a temperature of about 320 F. As is generally known, stretching of a polymer causes the crystalline structure to orient in the direction of the applied stress. This orientation results in an increase in tensile modulus and strain memory. Secondly, moreover, the stretching step further reduces the outside diameter of insulation 8, as well as the clearance between insulation 8 and tinsel conductor 2, to a figure of zero or marginally above zero. It is desirable not to stretch the insulated tinsel conductor so much that the insulation 8 is placed into gripping contact with the tinsel conductor 2, as this unduly restricts the tinsel ribbons.

A second viture of the stretching step is that an increase in insulated conductor length is achieved without use of further materials or sacrificing performance characteristics. The stretching is made possible by the compliance of the polymer insulation 8 and, rather surprisingly, the ready capability of all tinsel ribbon structures tested to undergo stretching without deformation. Tests have indicated that length increases from 8 to 10 percent in the stretching step are easily tolerated by the tinsel ribbon conductor.

Heat chamber 13 is, for example, an inductive heating coil, a gas-fired oven, or superheated steam, the preferred apparatus being superheated steam. Following chamber 13 is a conventional cooling trough 14 of the type such as cooling trough 9, which brings the insulated tinsel conductor temperature down to about 100 F. On leaving take-up capstan 12, the insulated and now stretched conductor is fed to a storage reel 15.

In later process steps, not shown, an outer jacket 16 is applied over a plurality of tinsel conductors around which the novel tubed insulation has been applied. Cordage of this type is used as the connection between the telephone station and a wall jack, for example.

The cord of FIG. 2 is highly advantageous as a retractile cord to impart the helical set to the cord of FIG. 2, the apparatus of FIG. 3 is typically used. The details for achieving the cord structure of FIG. 3 are as follows: An outer jacket 16, preferably polyvinyl chloride is applied over a plurality of the novel conductors. The jacketed cordage is wound on a mandrel and heat set in a circulating air oven, not shown, at a temperature approximately 10 percent less than the stretching temperature (320 degrees F.) for approximately 9 minutes. The heat set cord is removed from the mandrel and then the direction of the helix convolutions are reversed.

A method for producing a telephone cord of enhanced tensile modulus and strain memory has been described.

The cord structure is substantially reduced in outside diameter. The invention relies on stretching of both insulation and tinsel ribbon conductor in a step that involves reheating. The added cord length is a further benefit. The cord structure made from stretched polymer insulated tinsel conductors is useful in either coiled or straight cordage. The motion of the tinsel ribbon is not restricted within the primary insulation and hence the cord life is not affected.

The claims to follow embrace the spirit of the invention as above summarized, and define its scope.

What is claimed is:

1. In a process for manufacturing insulated tinsel conductors, the steps comprising:

tubing a polymer insulation over a strand of tinsel conductor with a clearance between the insulation and the conductor, and

thereafter concurrently stretching said insulation and said conductor while heating same to a temperature sufiicient to stress-orient the polymer crystalline structure.

2. Process pursuant to claim 1 wherein said polymer is a polyamide.

3. Process pursuant to claim 1 wherein said clearance is substantially .003 inch and wherein the subsequent stretching reduces said clearance to substantially .001 inch.

4. Process pursuant to claim 3 wherein said stretching increases the length of said insulation and said conductor by up to .10 percent.

5. Process pursuant to claim 4 wherein said polymer is a polyamide.

6. Method of making a retractable electrical cord comprising the steps of:

winding at least one tinsel ribbon around each of a plurality of support units;

tubing a polyamide insulation directly over each said wound tinsel conductor so as to maintain a first clearance between tube and tinsel conductor;

heating the resulting structure over an appreciable length thereof; and

stretching the heated structure a prescribed amount so as to draw down said tubes on said tinsel conductor to a second clearance between tube and tinsel conductor.

References Cited UNITED STATES PATENTS 201,477 3/ 1878 Alberger 15650 2,173,096 9/ 1939 Campbell 15650X 2,883,314 4/1959 Martin 156-50 3,413,167 11/1968 Trill 156-51 3,425,865 2/1969 Shelton 1565 6X FOREIGN PATENTS 866,169 4/ 1961 Great Britain 156-50 VERLIN R. PENDEGRASS, Primary Examiner 

